"Jacob Carlborg" <doob at me.com> wrote in message news:jthlpf$2pnb$1 at digitalmars.com... > > Can't "map" and "filter" return a random-access range if that's what they > receive? > map can, and does. filter cannot, because it doesn't know which element is number 4 until it knows if element 3 is included or not.